Molecular Scale Investigations Of Chromate Adsorption At The Mineral Water Interface

Chromate is a common groundwater contaminant as a result of extensive industrial use. The fate and transport of chromate in subsurface environments are largely governed by adsorption to the surfaces of aluminum and iron oxides. Characterization of adsorption mechanisms is needed to constrain thermodynamic models, better predict the fate and transport of environmental pollutants, and expand our fundamental knowledge of surface geochemistry. However, the mechanisms of chromate adsorption in soils have remained unclear. This dissertation clarifies the mechanisms by which chromate adsorbs to aluminum and iron oxide minerals on the basis of molecular spectroscopy and quantum mechanical calculations. Chromate adsorption was first characterized on ferrihydrite using in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR--FTIR) and theoretical frequency calculations. The effects of pH, aqueous chromate concentration, and ionic strength were investigated. It was determined that chromate primarily forms inner--sphere surface complexes on ferrihydrite. Monodentate complexes were observed to form at pH $>$ 6 and at low surface coverage under acidic pH conditions. Bidentate complexes are dominant below pH 6 and at high surface coverage. Theoretical infrared frequencies are in close agreement with those observed experimentally. Characterization of the chromate adsorption on hematite was performed using in situ ATR--FTIR spectroscopy and extended X--ray absorption fine structure (EXAFS) spectroscopy. The results were interpreted in the context of the optimized geometries and thermodynamics of the theoretical chromate--iron oxide cluster models. The results indicate that chromate binds to the surface of hematite in a similar manner as that of ferrihydrite; monodentate complexes dominate at high pH, and bidentate complexes dominate at low pH. The last system investigated was chromate adsorption on the surface of the aluminum oxyhydroxide boehmite. Both in situ ATR--FTIR and EXAFS spectroscopies were used to characterize chromate adsorption as a function of pH, ionic strength, and chromate and sulfate concentrations. It was determined that chromate primarily forms outer--sphere complexes on boehmite over a broad range of pH and chromate concentrations. Results from EXAFS and ATR--FTIR spectroscopy indicate the presence of a small fraction of inner--sphere chromate under acidic conditions.

Clearly explains how to more effectively decipher and predict contaminant fate in the environment by combining kinetic methods and molecular-scale spectroscopic and microscopic techniques to analyze mineral/water interfacial reactions in situ. The book begins with a broad overview, then continues with three sections written by internationally known expert. The first deals specifically with spectroscopic/microscopic techniques that can be used in combination with macroscopic approaches to glean mechanistic information on mineral/water reactions and processes. The second section emphasizes computer models that are used to elucidate surface mediated reaction mechanisms. The remainder of the volume is organized around reaction type, including sorption/desorption of inorganic species, sorption/desorption of organic species, precipitation/dissolution processes, heterogeneous electron transfer reactions, photochemically driven reactions, and microbially mediated reactions. Mineral-Water Interfacial Reactions will be a valuable resource for environmental scientists, geochemists, soil chemists, microbiologists, and marine engineers who need to be familiar with the most current and effective methods for testing and controlling the mobility, speciation, and bioavailability of contaminants in the environment.

Volume 23 of Reviews in Mineralogy and accompanying MSA short course covers chemical reactions that take place at mineral-water interfaces. We believe that this book describes most of the important concepts and contributions that have driven mineral-water interface geochemistry to its present state. We begin in Chapter 1 with examples of the global importance of mineral-water interface reactions and a brief review of the contents of the entire book. Thereafter, we have divided the book into four sections, including atomistic approaches (Chapters 2- 3), adsorption (Chapters 4-8), precipitation and dissolution (Chapters 9-11), and oxidation-reduction reactions (Chapters 11-14).

Based on the “International Symposium of Molecular Environmental Soil Science at the Interfaces in the Earth’s Critical Zone,” this book focuses on the Critical Zone supporting life at the Earth’s surface with emphasis on the new and emerging subject area of molecular environmental soil science. Advances in research methodology, the use of synchrotron radiation in particular, are extensively reviewed. Roles of microbes, biomolecules, and environmental nanoparticles in mineral transformations, metal cycling, degradation of natural and anthropogenic organic compounds are also extensively reviewed. It is unique in terms of facilitating the integration of contributions from traditionally separate disciplines and adding a molecular and nanoparticle (therefore chemical) dimension to a field of endeavour that has traditionally been viewed on a different scale (dimension). It will also contribute to identifying knowledge gaps, providing future research directions and promoting research and education at the molecular level in this extremely important and challenging area of science for years to come. The IUPAC Project Committee noted that the Conference identifies, and builds on, the need to view and understand the Critical Zone at the molecular level. The book will be an invaluable reference for research and education.

Provides an introduction to the chemistry of the solid-water interface, progressing from the simple to more complex and applied. Discusses the important interfaces in natural systems, especially geochemistry, in natural waters, soils and sediments. The processes occurring at mineral-water, particle-water and organism-water interfaces play critical roles in regulating the composition and ecology of oceans and fresh waters, the development of soils and plant nutrient's supply, preserving the integrity of water repositories and in such applications as water technology and corrosion science.

Unique in its comprehensive coverage of not only theoretical methods but also applications in computational spectroscopy, this ready reference and handbook compiles the developments made over the last few years, from single molecule studies to the simulation of clusters and the solid state, from organic molecules to complex inorganic systems and from basic research to commercial applications in the area of environment relevance. In so doing, it covers a multitude of apparatus-driven technologies, starting with the common and traditional spectroscopic methods, more recent developments (THz), as well as rather unusual methodologies and systems, such as the prediction of parity violation, rare gas HI complexes or theoretical spectroscopy of the transition state. With its summarized results of so many different disciplines, this timely book will be of interest to newcomers to this hot topic while equally informing experts about developments in neighboring fields.

Volume 49 of Reviews in Mineralogy and Geochemistry reviews the state of the art of synchrotron radiation applications in low temperature geochemistry and environmental science, and offer speculations on future developments. The reader of this volume will acquire an appreciation of the theory and applications of synchrotron radiation in low temperature geochemistry and environmental science, as well as the significant advances that have been made in this area in the past two decades. It gives a fairly comprehensive overview of synchrotron radiation applications in low temperature geochemistry and environmental science, describes the ways that synchrotron radiation is generated, including a history of synchrotrons and a discussion of aspects of synchrotron radiation that are important to the experimentalist, describes specific synchrotron methods that are most useful for single-crystal surface and mineral-fluid interface studies as well as methods that can be used more generally for investigating complex polyphase fine-grained or amorphous materials, including soils, rocks, and organic matter.

Volume 40 of Reviews in Mineralogy and Geochemistry compiles and synthesizes current information on sulfate minerals from a variety of perspectives, including crystallography, geochemical properties, geological environments of formation, thermodynamic stability relations, kinetics of formation and dissolution, and environmental aspects. The first two chapters cover crystallography (Chapter 1) and spectroscopy (Chapter 2). Environments with alkali and alkaline earth sulfates are described in the next three chapters, on evaporites (Chapter 3), barite-celestine deposits (Chapter 4), and the kinetics of precipitation and dissolution of gypsum, barite, and celestine (Chapter 5). Acidic environments are the theme for the next four chapters, which cover soluble metal salts from sulfide oxidation (Chapter 6), iron and aluminum hydroxysulfates (Chapter 7), jarosites in hydrometallugy (Chapter 8), and alunite-jarosite crystallography, thermodynamics, and geochronology (Chapter 9). The next two chapters discuss thermodynamic modeling of sulfate systems from the perspectives of predicting sulfate-mineral solubilities in waters covering a wide range in composition and concentration (Chapter 10) and predicting interactions between sulfate solid solutions and aqueous solutions (Chapter 11). The concluding chapter on stable-isotope systematics (Chapter 12) discusses the utility of sulfate minerals in understanding the geological and geochemical processes in both high- and low-temperature environments, and in unraveling the past evolution of natural systems through paleoclimate studies. The review chapters in this volume were the basis for a short course on sulfate minerals sponsored by the Mineralogical Society of America (MSA) November 11-12, 2000 in Tahoe City, California, prior to the Annual Meeting of MSA, the Geological Society of America, and other associated societies in nearby Reno, Nevada. The conveners of the course (and editors of this volume of Reviews in Mineralogy and Geochemistry), Alpers, John Jambor, and Kirk Nordstrom, also organized related topical sessions at the GSA meeting on sulfate minerals in both hydrothermal and low-temperature environments.